Digital Subscriber Loop, or DSL, is one of the most promising new technologies for delivering superior service and higher speed connections over existing infrastructure in the telecommunications industry. Recent changes in the telecommunications industry such as the deregulation of local markets has brought on the emergence of new technologies such as DSL. In addition, the growing demand for faster, more reliable Internet access has increased the demand for technologies that deliver higher speed connections over existing infrastructure.
In general, DSL uses the existing copper loop that is currently used for conventional telephony to deliver data at high bandwidth. Currently, the transmission rates for DSL technologies are dependent on the distance between a central office and a particular customer. Moreover, depending on the type of DSL technology, the transmission rate downstream to the customer and upstream to the central office may vary. For example, for asymmetric DSL, the transmission rate is faster downstream to the customer than upstream to the central office, and thus is well suited for Internet usage and video on demand. On the other hand, for symmetric DSL, the transmission rate is about the same for both downstream and upstream.
As is well known, DSL uses packet switching technology that operates independently of voice telephone system, allowing telephone companies to provide Internet service and not lock up circuits for telephone calls. DSL can carry both voice and data signals simultaneously, in both directions, allowing the customer to log onto the Internet and make a telephone call at the same time. Thus, it is easy to understand why DSL is becoming the preferred system and method for sending/receiving analog and digital data/signals in the telecommunications industry.
One major problem for those in this industry is the installation and maintenance of DSL using the existing infrastructure and standard operational tools. This problem is better understood by first describing the installation/testing process in a conventional POTS (plane old telephone system) environment, which is described in greater detail hereinafter with reference to FIGS. 1-3.
FIG. 1 illustrates a simplified diagram of a POTS environment having a butt set connected to a copper loop for maintenance and testing purposes. In the conventional POTS environment, a central office (CO) 2 is connected to a customer's telephone 8 at the customer's premise 6 (home, office, etc.) using a copper loop 4 (pair of copper wires). In between the CO 2 and the customer's premise 6, a field technician 12 uses a conventional butt set 10 or any other maintenance instrument to test the copper loop. The butt set 10 is generally a standardized device that the technician 12 uses to determine which copper loop is active and/or available for customers. The butt set 10 is essentially a portable and rugged telephone set. For example, once the butt set 10 is connected to a cooper loop via electrical clips, the technician 12 can simulate a telephone going off-hook to draw audible tones. A voice switch (not shown) in the CO 2 recognizes an off-hook condition through its loop supervision circuit and applies audible tones to the loop allowing the technician 12 to confirm proper connectivity.
The butt set 10 illustrated herein is equivalent to a telephone handset to test/maintain communication wires. The term butt set is used in this field, presumably because the butt set 10 includes a hook for fastening it to a tool belt and tends to hand down along the technician's buttocks. The butt set 10 generally includes a microphone, earphone, and a speaker.
FIG. 2 illustrates a diagram of an existing circuit used in the POTS environment as shown in FIG. 1. The CO 2 typically includes a SLIC (subscriber loop interface circuit) 20 for interfacing with a pair of wires, tip and ring, from the outside plant. The SLIC 20 includes an amplifier AT 22 connected in series to a resistor R.sub.b1 26, and an amplifier AR 24 connected in series to a resistor R.sub.b2 28. The amplifier AT 22 and resistor R.sub.b1 26, and the amplifier AR 24 and resistor R.sub.b2 28 form a balance drive interface circuit to the tip and ring wires. As known, the SLIC 20 can be implemented with transformers instead of amplifiers AT 22, AR 24. Further connected in between the resistor R.sub.b1 26 and the resistor R.sub.b2 28 is a detector 30. Typically, the ohm values of the resistors R.sub.b1 26 and R.sub.b2 28 are equal (50 to 400 ohms). The voltage V.sub.b is the effective battery voltage across the tip and ring wires.
The detector outputs a signal voltage V.sub.s (which is proportional to the DC current flow in the loop, which in turn is proportional to the length of the loops and is reflected as resistance) into a comparator C32, while a reference voltage V.sub.r is also inputted into the comparator C32. The comparator C32 then outputs a loop status indication signal (SHD) based on voltages V.sub.s and V.sub.r.
In the outside plant, there also exist resistors R.sub.11 34 and R.sub.12 36, where each resistor is connected in series to the tip and ring wires, respectively. As is well known, tip and ring are terms used to describe the two wires that are used to set up a telephony/DSL connection. Typically, the ohm value of resistors R.sub.11 34 and R.sub.12 36 are the same, which is also dependent on the length of the loop.
In the customer's premise 6, the telephone 8 can be represented with an off-hook switch S.sub.p 38 connected in series with a resistor R.sub.p 40. The resistor R.sub.p 40 typically has a value of, preferably, between 100 to 200 ohms (off-hook resistance is less than or equal to 400 ohms). Further, the sum of the resistors R.sub.11 34, R.sub.12 36, and R.sub.p 40 should be less than or equal to 1900 ohms, as per conventional telephony standards.
The butt set 10 includes a monitor mode switch S.sub.m 50 connected in series with a monitor mode resistor R.sub.m 52 (typically greater than 100 K ohms), which switch S.sub.m 50 and resistor R.sub.m 52 are further connected in parallel with a talk mode switch S.sub.t 54 and a talk mode resistor R.sub.t 56 (typically less than 400 ohms). Thus, the butt set 10 can provide two different modes of operation, as described in greater detail hereinafter. The butt set 10 also includes two leads, where one lead is connected to the tip at position a and the other lead is connected to the ring at position a'.
During operation in the POTS environment, a battery is used to provide a DC path or current flow beginning from the amplifier AT 22 through resistors R.sub.b1 26, R.sub.11 34, R.sub.p 40, R.sub.12 36, R.sub.b2 28 to the amplifier AR 24. Thus, the current flowing through this circuit is inversely proportional to the sum of the resistors R.sub.b1 26, R.sub.11 34, R.sub.p 40, R1.sub.2 36, and R.sub.b2 28. When the customer picks up the telephone 8 to make a call, the detector 30 detects that the telephone 8 is off hook, a DC path is generated, and the CO 2 recognizes an off-hook condition, thereby providing a dial tone to the customer. In this environment, the frequency signals in the copper loop operate within the voice/audio bandwidth and the DC current path is used for loop supervision.
During the maintaining, testing, or installing stage, the technician 12 uses the butt set 10 to connect to the tip and ring wires at points a, a'. The butt set 10 is ideal for using in the POTS environment since it is designed to perform all the standard telephone functions. The technician 12 first determines whether any or both the wires on the copper loop are live or dead using the butt set 10.
When the butt set 10 is switched in the monitor mode, a high impedance voltmeter (not shown) equivalent can be used to determine the existence of proper DC voltages to indicate a live loop. In addition, in the monitor mode, the technician 12 can listen for audio tones on the wires, which is another indication of whether the wires are alive or dead. When the technician 12 desires to use the copper pair to talk to someone at the CO 2, the butt set 10 can be switched to talk mode using switch S.sub.t 54 and the resistor R.sub.t 56, which is similar to the resistor R.sub.p 40 in the telephone 8. The CO 2 then generates a dial tone for the technician 12 so that he/she can make a call.
The conventional testing and maintaining method is generally acceptable in the POTS environment, but as will be described below, it is inadequate in testing, maintaining, and installing in the DSL environment.
FIG. 3 illustrates a simplified diagram of a DSL environment having a butt set connected to a copper loop. In the DSL environment, the CO includes a DTU-C (DSL termination unit--CO) 102 having capacitors C 104 and inductors 106. One end of the copper loop is connected to the DTU-C 102 at point TR2 and the other end is connected to the customer's premise at point TRI. The customer's premise also includes a DTU-R (DSL termination unit--remote) 120 having capacitors 122 and inductors 124.
In the DSL environment, the conventional system and method using the butt set 10 is generally inadequate for testing/maintaining/installing. It is well known that in the DSL environment no DC path or current flow is possible since a battery ("dry circuit") is not used at the CO, and thus, the butt set 10 will typically not function properly under this environment. For example, the butt set 10 can not detect the presence of a DC voltage since no battery is present As a result, there is no loop status supervision in this environment.
Further, there is no mechanism to access/draw/detect audible tones in this environment because DSL signals operate at frequency above voice/audio bandwidth. Thus, field technicians have a difficult time testing/maintaining/installing the outside copper loop using the conventional instrumentation. For example, technicians can not determine whether a copper loop is alive or dead using the conventional butt set 10, which in many cases, results in removing live copper loops from service. As a result, the technician make mistakes such as improperly connecting the copper loop to the CO and disconnecting a "good service" from an existing DSL customer.
Accordingly, there is a need for a system and method for providing a reliable and effective manner of testing, maintaining, and installing a copper loop in the DSL environment. There is also a need for implementing a system and method for maintaining, testing, and installing in the DSL environment using conventional butt sets.